Vacuum interrupters are used for reliable interruption of fault current and load breaking in the electrical distribution systems. Vacuum interrupters have gained importance as compared with air, oil or SF6 filled current interrupting devices because of their reliability and compactness. The vacuum interrupters can be encapsulated for improved performance, compactness and better dielectric withstandability. Encapsulation of the vacuum interrupter herein refers to casting or potting of the vacuum interrupter with the encapsulating material such as silicone rubber.
Vacuum interrupters are embedded in epoxy resin to form poles of indoor circuit breakers. However, for outdoor circuit breakers, vacuum interrupters are assembled in porcelain or ceramic housings. The external dielectric creepage specification of a vacuum interrupter is overcome by encapsulating a layer of insulating material over the entire vacuum interrupter. Encapsulation can be done in a manner by which the metallic parts which are either at high potential or floating potential or earth potential are masked. Bonding agents can be used between the ceramic and the insulating material for proper adhesion.
Vacuum interrupters can be encapsulated to achieve advantages that are derived from increasing the creepage distance and clearance, and from decreasing high stress zones and non uniform stress zones. These are some of the exemplary considerations that are accounted for when encapsulating vacuum interrupters. However, in current practice with an attempt to achieve the above, the entire vacuum interrupter is encapsulated, by which the weight of the vacuum interrupter increases and by which an increase in the cost can occur along with other aspects that are encountered during the process of encapsulation. Moreover, the electric field intensity can increase, due to which the stress region is continuous from the pole top terminal to the bottom of the ceramic housing of the vacuum interrupter. This continuous stress region which is on the internal surface of the porcelain/ceramic housing of the outdoor vacuum circuit breaker can cause surface dielectric failure.
Owing to the above, exemplary embodiments disclosed herein are directed to encapsulation of the vacuum interrupter through a better design, and to providing a solution for encapsulating the vacuum interrupter and to catering to advantages of such encapsulation.